Element Z has an atomic number of 17.
In a sample of Z there are two isotopes. One isotope has a mass number of 35 and the other isotope has a mass number of 37.
All atoms of element Z in this sample contain:
17 protons
17 neutrons
18 protons
18 neutrons
87 exam-style questions on Edexcel GCSE Chemistry 2.1 Atomic structure, covering 2.1.1 Development of the atomic model, 2.1.2 Structure of the atom and subatomic particles, 2.1.3 Mass number, isotopes and relative atomic mass, and 2.1.4 Calculating relative atomic mass from isotopic abundance. Each one has a worked solution and a mark scheme showing where the marks go.